Since the position determination is very decisive for the execution of planned missions, it is especially important to increase the reliability of such systems. The star sensors consist of a lens system, a light-sensitive matrix detector and an evaluation unit for computing position information of the flying object by comparing the detected sky sections to a star catalog that is based on an inertial system. The use of several star sensors in a system enhances the reliability as well as the precision of the position measurement.
The determination of the position of such flying objects such as, for example, satellites, space stations, space shuttles and the like is made by means of a method that evaluates the data from one or more star sensors which are oriented with respect to a given area of the sky—referred to below as sky sections—by means of a prescribed field of view, and which use image recognition to compare the sky section that was detected in a matrix detector to a star catalog stored in a memory. After the association of the sky section, the position of the flying object is determined in that, for example, the Euler angle and/or quaternions are determined according to the QUEST algorithm from the measured star vectors and from the data of the star catalog, after which they are transformed from the coordinate system of the sensor system into the coordinate system of the flying object. The more stars evaluated in the sensor system, the greater its measuring precision. By orienting the individual sensors in different viewing directions, it is achieved that the errors of the three solid angles (Euler angles) are of approximately the same magnitude and are minimal.
European patent application EP 1 111 402 A1 discloses a sensor system in which three star sensors are arranged with their fields of view oriented in different directions, whereby each star sensor detects the star positions and outputs this to a central evaluating device in which the position of the sensor system is determined and the position of the flying object is determined on the basis of the orientation of the sensor system relative to a flying object. In order to avoid additional errors, the star cameras are located on a solid block.